Extruders of rigid PVC compounds and other thermoplastic are constantly seeking ways to increase output rates through the purchase of larger extrusion equipment, the redesign of existing equipment or the redesign of formulations using new or improved process aids. Improved output rates result in more economical plant operations that lead to greater profitability for the thermoplastic converters.
Thermoplastic formulations contain a variety of additives, including process aids (both conventional and lubricating), and internal and external lubricants, designed to increase throughput. Typically external lubricants and certain types of process aids, generically described as lubricating process aids may reduce melt viscosity in PVC formulations. Lubricating process aids are typically low molecular weight polymers that have a lubricating function built into the polymer backbone. Generally today's rigid PVC formulations are run without lubricating process aids. Conventional process aids typically used in rigid PVC formulations are high molecular weight polymers, with molecular weights significantly higher than PVC resin and cause increases in melt torque depending on their molecular weight.
In WO/093565, Applicant disclosed a method whereby impact modifiers and mineral fillers were co-dried, resulting in a hybrid impact modifier that overcame problems of dispersion and concentration heterogeneities seen when the dry components were blended.
Applicant has now found that co-powderizing aqueous streams or an aqueous blend of polymeric process aids and mineral fillers results in a composite material in which the dry composite consists of complex particles that contain both the polymer and inorganic phases in an intimate mixture.